Olefins, perfluoroalkylated

In addition to the arenes, enolates, and other nucleophiles depicted in Scheme 2.142, FITS reagents are also reactive in the perfluoroalkylation of unactivated alkenes, alkadienes [19], and acetylenes [20] (Scheme 2.146). In contrast with olefin perfluoroalkylation by means of perfluoroalkyl bromides or iodides (Section 2.2.1), this reaction does not follow a free radical mechanism but proceeds via cationic intermediates which can be either trapped by addition of nucleophiles or nucleophilic solvents or quenched by -deprotonation with a base (Scheme 2.147). 

Synthetic oils have been classified by ASTM into synthetic hydrocarbons, organic esters, others, and blends. Synthetic oils may contain the following compounds diaLkylben2enes, poly(a-olefins) polyisobutylene, cycloaUphatics, dibasic acid esters, polyol esters, phosphate esters, siUcate esters, polyglycols, polyphenyl ethers, siUcones, chlorofluorocarbon polymers, and perfluoroalkyl polyethers. 

Alkylated aromatic lubricants, phosphate esters, polyglycols, chlorotrifluoroethylene, siUcones, and siUcates are among other synthetics that came into production during much that same period (28,29). Polyphenyl ethers and perfluoroalkyl polyethers have followed as fluids with distinctive high temperature stabiUty. Although a range of these synthetic fluids find appHcations which employ their unique individual characteristics, total production of synthetics represent only on the order of 2% of the lubricant market. Poly(a-olefin)s, esters, polyglycols, and polybutenes represent the types of primary commercial interest. 

The fluoroalkyl hypochlorites readily react with GO and SO2 to form the corresponding chloroformates and chlorosulfates in near quantitative yields (270). They add to olefins giving a-chloroethers (271). Borate esters are obtained by reaction of perfluoroalkyl hypochlorites with BGl (272). 

Additions of halogen fluorides to the more electrophilic perfluonnated olefins generally require different conditions Reactions of iodine fluoride, generated in situ from iodine and iodine pentafluoride [62 102 103, /05] or iodine, hydrogen fluoride, and parapeiiodic aud [104], with fluormated olefins (equations 8-10) are especially well studied because the perfluoroalkyl iodide products are useful precursors of surfactants and other fluorochemicals Somewhat higher temperatures are required compared with reactions with hydrocarbon olefins Additions of bromine fluoride, from bromine and bromine trifluonde, to perfluonnated olefins are also known [lOti]... 

Other well-known reactions are those offluorinated olefins with fluoride ion and negatively substituted aromatic compounds leading to the formation of per-fiuoroalkylated aromatic compounds The reaction may be considered an amonic version of a Fnedel Crafts process and can result in introduction of one or several perfluoroalkyl substituents [/ /] Aromatic substrates include substituted and unsuhstiluled perfiuorobenzenes [J3l, 212, 213, 214], fiuorinated heterocycles [131, 203, 215, 216, 217, 218, 219, 220, 221, 222, 223],perchlorinated heterocycles [224] (equation 44), and other activated aromatic compounds [225] (equation 45) The fluonnated olefins can be linear or cyclic [208] (equation 46)... 

A more efficient agent than peroxy compounds for the epoxidation of fluoro-olefins with nonfluonnated double bond is the hypofluorous acid-acetomtrile complex [22] Perfluoroalkylethenes react with this agent at room temperature within 2-3 h with moderate yields (equation 13), whereas olefins with strongly electron-deficient double bond or electron-poor, sterically hindered olefins, for example l,2-bis(perfluorobutyl)ethene and perfluoro-(l-alkylethyl)ethenes, are practically inert [22] Epoxidation of a mixture of 3 perfluoroalkyl-1-propenes at 0 C IS finished after 10 mm in 80% yield [22] The trifluorovinyl group in partially fluorinated dienes is not affected by this agent [22] (equation 13)... 

The reactivities of the substrate and the nucleophilic reagent change vyhen fluorine atoms are introduced into their structures This perturbation becomes more impor tant when the number of atoms of this element increases A striking example is the reactivity of alkyl halides S l and mechanisms operate when few fluorine atoms are incorporated in the aliphatic chain, but perfluoroalkyl halides are usually resistant to these classical processes However, formal substitution at carbon can arise from other mecharasms For example nucleophilic attack at chlorine, bromine, or iodine (halogenophilic reaction, occurring either by a direct electron-pair transfer or by two successive one-electron transfers) gives carbanions These intermediates can then decompose to carbenes or olefins, which react further (see equations 15 and 47) Single-electron transfer (SET) from the nucleophile to the halide can produce intermediate radicals that react by an SrnI process (see equation 57) When these chain mechanisms can occur, they allow reactions that were previously unknown Perfluoroalkylation, which used to be very rare, can now be accomplished by new methods (see for example equations 48-56, 65-70, 79, 107-108, 110, 113-135, 138-141, and 145-146)... 

Replacement of iodine in (perfluoroalkyl)ethyl iodides predominates over the usual conversion to olefins when the reagent is very nucleophilic and weakly basic Soft nucleophiles like sodium thiocyanate and sodium thiolates react well in displacements [46, 47] (equation 42)... 

Perfluoroalkylation of olefins and acetylenes occurs in low yields when perfluoroalkylcopper reagents are heated with alkenes or acetylenes in DMSO [226, 237, 238, 239]. Undine derivatives react similarly [240]... 

Perfluoroalkylation of perfluoroalkylethylenes and addition of perfluoroalkyl iodides to olefins or acetylenes are catalyzed by copper metal [238, 239] Similar copper-catalyzed addition of iododifluoroacetates to olefins has been observed [241]... 

The reaction of perfluoroalkyl iodides with electron donor nucleophiles such as sodium arene and alkane sulfinates in aprotic solvents results in radical addition to alkenes initiated by an electron-transfer process The additions can be carried out at room temperature, with high yields obtained for strained olefins [4 (equations 3-5)... 

The activity of homogeneous catalysts also has been demonstrated Wilkin son s catalyst trisftriphenylphosphme rhodium chloride induces perfluoroalkyl iodides to add to olefins at 80 [70] (equation 10) Tetrakis(triphenylphosphine)-... 

The olefin yields are higher with 2-(perfluoroalkyl) ethane iodides than their hydrocarbon analogues apparently because of the strongly electron withdrawing fluorine making the hydrogens more acidic and prone to elimination. 

The addition of perfluoroalkyl iodides to simple olefins has been quite successful under aqueous conditions to synthesize fluorinated hydrocarbons.119 In addition to carbon-based radicals, other radicals such as sulfur-based radicals, generated from RSH-type precursors (R = alkyl, acyl) with AIBN, also smoothly add to a-allylglycines protected at none, one, or both of the amino acid functions (NH2 and/or CO2H). Optimal results were obtained when both the unsaturated amino... 

The procedure illustrates a fairly general method for the preparation of -substituted perfiuoroolefins. The method has been applied to the synthesis of 2-cyclohexyl- (70%), 2-benzyl- (61%), and 2-(/>-fluorophenyl)perfluoropropenes (67%), and it is probably applicable to any a-trifluoromethyl ketone. Olefins containing a perfluoroalkyl group other than trifluoromethyl can be prepared by the same procedure by the substitution of lithium chlorodifluoroacetate for sodium chlorodifluoroacetate.7 Other routes to / -substituted perfiuoroolefins are not general or convenient. Routes to perfiuoroolefins generally yield the a-substi-tuted olefin rather than the /3-substituted olefin. 

This method can also be utilized as a general method for the preparation of olefins with terminal difluoromethylene groups from aldehydes.8 Also, by the substitution of tributylphosphine for triphenylphosphine in this procedure, ketones other than those containing an a-perfluoroalkyl group can be converted to terminal difluoromethylene compounds.9... 

In contrast to the direct reduction as described above, the indirect electrochemical reduction of perfluoroalkyl halides is a versatile and novel method for generating perfluoroalkyl radicals selectively. Saveant et al. have demonstrated many successful examples. Using terephthalonitrile as a mediator, the indirect reduction of CF3Br in the presence of styrene leads to the dimer of the radical adduct obtained by the attack of CF on styrene. On the other hand, in the presence of butyl vinyl ether, the mediator reacts with the radical adduct obtained by the attack of CF3. on the olefin (Scheme 3.4) [14]. 

WITTIG OLEFINATION OF PERFLUOROALKYL CARBOXYLIC ESTERS SYNTHESIS OF 1,1,1-TRIFLUORO-2-ETHOXY-5-PHENYLPENT-2-ENE AND 1-PERFLUOROALKYL EPOXY ETHERS 1,1,1-TRIFLUORO-2-ETHOXY-2.3-EPOXY-5-PHENYLPENTANE (Oxirane, 2-ethoxy-3-(2-phenylethyl)-2-(trifluoromethyl)-, cis-(+)-)... 

Not much is known about the reactivity of the phosphinocarbene 2i. Problems arise, at least in part, from the high 1,3-dipolar reactivity of the diazo precursor li, which hides any carbene reactivity. Indeed, although li is stable in a toluene solution at 60°C for hours, the addition of an electron-poor olefin, such as a perfluoroalkyl-monosubstituted alkene, induces the exclusive formation of the thermodynamically more stable anti-isomer of the cyclopropane 14 (see Section V,B,3,a).36 This clearly demonstrates that the cyclopropanation reaction does not involve the carbene 2i, but that an initial [2 + 3]-cycloaddition occurs leading to the pyrazoline 13, which subsequently undergoes a classical N2 elimination.37... 

Fig. 19 Cathodic carboxylation of perfluoroalkyl olefins with subsequent fluoride elimination [107].

The kinetic data for halogenated carbon-centred radicals with silicon hydrides are also numerous and a few examples are shown in Table 3.2. The kinetic data for perfluoroalkyl radicals were obtained by competition of the appropriate silane with the addition to an olefin [16-18]. The kinetic deuterium isotope effects (/ h/ d) on the attack of on the Si—D bond of... 

Progress in the areas of photoscrambling and valence bond isomerization reactions in aromatic156 and heteroaromatic compounds157 has led to the study of new cyclic systems with strained olefinic double bonds.158 Dewar benzene, Dewar thiophene, benzvalene, and their heteroaromatic counterparts substituted with fluoro and/or perfluoroalkyl substituents have been synthesized and their reactions with phenyl azide have been investigated. 

---